Nonaqueous electrolyte secondary batteries such as a lithium-ion secondary battery are in wide use as batteries for devices such as a personal computer, a mobile telephone, and a portable information terminal. Among those, attention is being given to the lithium-ion secondary battery as a battery that reduces carbon dioxide emissions and contributes to energy saving, as compared with conventional secondary batteries.
Conventionally, separator rolls in each of which a nonaqueous electrolyte secondary battery separator is wound around a core have been developed. In addition, studies are being carried out in regard to checking for detecting foreign substances adhering to the separator roll.
As an example of check for detecting foreign substances adhering to a target object, a technique is disclosed in Patent Literature 1. In the technique disclosed in Patent Literature 1, an X-ray emitted from an X-ray source is converted into parallel X-rays by a capillary lens, then a sample which is a target object is irradiated with the parallel X-rays, and then a time delay integration (TDI) sensor receives the parallel X-rays which have passed through the sample. The TDI sensor employs, for example, a technique disclosed in Patent Literature 2.
In a case of detecting foreign substances adhering to a target object having a surface whose profile is a circle (e.g., a lateral surface of a separator roll), the following checking method may be employed. Note that, hereinafter, the surface of the target object whose profile is a circle is also referred to as “circular profile surface”.
That is, the target object is rotated about an axis that (i) passes through a center of a circle constituting a profile of the circular profile surface and (ii) extends in a direction substantially perpendicular to the circular profile surface. Then, the circular profile surface is irradiated with an electromagnetic wave. Then, a sensor receives the electromagnetic wave which has passed through the circular profile surface. Then, images obtained when the sensor has received the electromagnetic wave are analyzed, and thus whether foreign substances are adhering to the target object or not is checked. From this, the detection of foreign substances can be carried out highly efficiently, and this makes it possible to enhance a speed of the check, as compared with the technique disclosed in Patent Literature 1.